[PATCH 6.1 275/473] af_packet: do not call packet_read_pending() from tpacket_destruct_skb()

Greg Kroah-Hartman
2024-06-06T14:17:01Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 581073f626e387d3e7eed55c48c8495584ead7ba ]

trafgen performance considerably sank on hosts with many cores
after the blamed commit.

packet_read_pending() is very expensive, and calling it
in af_packet fast path defeats Daniel intent in commit
b013840810c2 ("packet: use percpu mmap tx frame pending refcount")

tpacket_destruct_skb() makes room for one packet, we can immediately
wakeup a producer, no need to completely drain the tx ring.

Fixes: 89ed5b519004 ("af_packet: Block execution of tasks waiting for transmit to complete in AF_PACKET")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Neil Horman <nhorman@tuxdriver.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20240515163358.4105915-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/packet/af_packet.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 7188ca8d84693..8888c09931ce3 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2528,8 +2528,7 @@ static void tpacket_destruct_skb(struct sk_buff *skb)
ts = __packet_set_timestamp(po, ph, skb);
__packet_set_status(po, ph, TP_STATUS_AVAILABLE | ts);

- if (!packet_read_pending(&po->tx_ring))
- complete(&po->skb_completion);
+ complete(&po->skb_completion);
}

sock_wfree(skb);
--
2.43.0